1. Field of the Invention
The present invention relates to a differential signal transmission cable including a pair of conductive wires that transmit differential signals and a multi-core differential signal transmission cable including a plurality of differential signal transmission cables.
2. Description of the Related Art
Differential signal transmission cables used for high-speed digital communication at several gigahertz or more between information processing apparatuses, such as computers, and multi-core differential signal transmission cables which each include a plurality of differential signal transmission cables are known. Some of these differential-signal cables have a structure for suppressing suck-out, which is a phenomenon that signals attenuate in a high-frequency band (see, for example, Japanese Unexamined Patent Application Publication No. 2012-18764 (hereinafter referred to as Patent Document 1)).
Patent Document 1 describes a differential signal transmission cable in which a pair of signal lines arranged parallel to each other are covered with an insulator and the outer periphery of the insulator is covered with a first piece of composite tape and a second piece of composite tape. The first and second pieces of composite tape each include a vapor-deposited metal layer, and are wrapped around the insulator such that the respective vapor-deposited metal layers are in contact with each other. The first piece of composite tape is helically wrapped around the outer periphery of the insulator with the vapor-deposited metal layer thereof facing outward. The second piece of composite tape is longitudinally wrapped around the outer periphery of the first piece of composite tape with the vapor-deposited metal layer thereof facing inward.
Since the first piece of composite tape is helically wrapped around the outer periphery of the insulator, a gap between the insulator and the first piece of composite tape is reduced. Accordingly, a difference in propagation delay time between the pair of signal lines, that is, an intra-pair skew, is reduced. Since the second piece of composite tape is longitudinally wrapped around the outer periphery of the first piece of composite tape such that the vapor-deposited metal layers are in contact with each other, a shield current flows through the first and second pieces of composite tape in a longitudinal direction of the pair of signal lines. As a result, the suck-out is suppressed.